If you need one, take a look at this one:
“A free, full-featured, graphically laid out, high-precision, scientific calculator for Mac OS X 10.4 and greater. Full source-code is included with the distribution.
Ideal if you need to enter large expressions or have accurate precision. “Data” drawers allow an easy way to generate statistical data, linear regression and gaussian elimination. The extensive support of complex numbers and hexadecimal numbers is also a significant benefit for anyone who has to work with this type of data.”